History copying optimization and/or UX improvement

> if you have a sufficiently large collection (in my case 300+ datasets) it takes >10 min to copy it into a new history. crazy

edit:
Related to: #2526

> [nekrut] but process continues in the background, so eventially it does get copied, but why soooooooooo long?

Reproduce copying a history containing 300 or more datasets and compare the behavior described in the issue. Review related issue #2526 and clarify whether the accepted outcome is faster copying, improved progress feedback, or both; done should be a measurable improvement or clearly communicated background progress.

Written by the indexing model from the issue text.